1. Technical Field
The present invention relates to a method of manufacturing an organic electroluminescence device.
2. Related Art
In recent years, with the diversification of information apparatuses, etc., there have been increased needs for flat display devices with low power consumption and reduced weight. As one type of such flat display devices, organic EL devices have been proposed, in which organic electroluminescence (hereinafter referred to as “organic EL”) elements having organic functional layers, such as a luminescent layer and a hole transport layer, emit light so that a display operation is performed.
Two types of organic EL devices are known: namely, a top emission type in which light emitted by organic EL elements is extracted from a side opposite the substrate having the organic EL elements, and a bottom emission type in which light is extracted from the substrate side. When these two emission types are compared, in the organic EL device of a top emission type, the pixel aperture ratio can be easily increased, which is advantageous in achieving higher definition and higher quality of displayed images.
In an organic EL device of a top emission type, an electrode (cathode), which is located on the side from which light from the luminescent layer is emitted, is formed so as to be light-transmissive. Specifically, a light-transmissive electrode (transparent cathode) is formed by a method in which a transparent conductive material, such as indium tin oxide (ITO), is used, or by a method in which, using a metal material, such as silver or aluminum, a thin film is formed with a small thickness to such an extent that light transmission is achieved.
However, such a transparent cathode has high electrical resistance due to physical properties of the constituent material itself and the small conductor cross-sectional area of the thin, transparent cathode. Consequently, the value of current flowing into the organic EL elements provided in the organic EL device may change depending on the position where the elements are placed, resulting in occurrence of display unevenness, such as uneven light emission and uneven luminance, in displayed images.
Under these circumstances, there have been proposals to eliminate display unevenness by forming an auxiliary line that assists electrical conduction so that the electrical resistance of the entire electrode including the transparent cathode and the auxiliary line is substantially decreased. For example, JP-A-2003-123988 and JP-A-2001-195008 each disclose a configuration in which an auxiliary line composed of a metal material having low resistance, such as aluminum or chromium, is formed on the top surface of a partition wall surrounding organic EL elements, and a transparent cathode is formed over the entire surface so as to overlie the auxiliary line.
Meanwhile, the manufacturing method of the organic EL element differs depending on whether the organic functional layer is formed using a low-molecular-weight material or a high-molecular-weight material. In many cases, low-molecular-weight materials contain molecules with a rigid skeleton and have low solubility in an organic solvent. Therefore, when a low-molecular-weight material is used for the organic functional layer, vapor phase reaction, such as vacuum deposition, is used. On the other hand, in many cases, high-molecular-weight materials have relatively high solubility in an organic solvent. Therefore, when a high-molecular-weight material is used for the organic functional layer, a wet coating method is used in which a liquid (functional liquid) containing an organic functional layer-forming material is applied/placed at a predetermined position, and the solvent is evaporated, thereby to form a film (functional film) composed of a desired material.
One of known examples of the wet coating method that can be effectively used for the manufacture of organic EL elements is a liquid droplet ejection method. In particular, an ink jet method has various advantages, such as there being no need for use of a mask in patterning, having a capability of applying different types of liquids with high resolution, there being little loss of ink, and ease of large area coating. Consequently, the ink jet method is suitable for forming a functional film in which a fine pattern, for example, a fine RGB pattern for full-color display, is formed using different liquids, and thus it is possible to obtain a high-resolution, high-quality organic EL device.
In the manufacturing method using the liquid droplet ejection method, in order to define regions in which the respective functional liquids are to be placed, a partition wall is disposed so as to surround each region to which the corresponding functional liquid is to be applied. By providing the partition wall, positional accuracy can be improved, and an applied functional liquid can be prevented from being mixed with a functional liquid applied to another region. In order to ensure patterning, desirably, the partition wall has liquid-repellency with respect to the functional liquids, and the regions to which the functional liquids are applied have liquid-affinity with respect to the functional liquids.
However, when an organic EL device having an auxiliary line provided on the partition wall is manufactured using the liquid droplet ejection method, the following problems arise. That is, when the liquid droplet ejection method is carried out using the partition wall, the top surface of the partition wall is required to be kept liquid-repellent in order to ensure patterning. However, if the auxiliary line is formed using a metal material, the top surface of the partition wall becomes liquid-philic, which may result in difficulty in performing a reliable patterning process.